Analysis of blood samples from 300 people in Utah did not show an association between chronic fatigue syndrome and infection with XMRV retrovirus.

Some prior research has indicated that xenotropic murine leukemia virus-related virus (XMRV) and other murine leukemia virus (MLV) relatives are common in people with chronic fatigue syndrome (CFS), prostate cancer, and other conditions. CFS is characterized by overwhelming fatigue that does not improve with rest.

In particular, a study by Judy Mikovits from the Whittemore Peterson Institute and colleagues, published in the October 23, 2009, issue of Science, found that 67% of CFS patients had detectable XMRV in peripheral blood mononuclear cells, compared with just 4% of people without chronic fatigue.

These findings have led some CFS patients to use antiretroviral drugs developed for HIV on an off-label basis, and advocates have urged that clinical trials be started for this new patient population.

Study results have not been consistent, however, and other research teams have found no association between CFS and XMRV or related viruses.

In an effort to resolve this conflict, Clifford Shin and Ila Singh from the University of Utah and colleagues collected and analyzed blood samples from 100 CFS patients and 200 healthy volunteers from the Salt Lake City area, using molecular, serological, and viral growth assays. A majority (70%) of the CFS patients reported flu-like symptoms at the onset of fatigue, suggestive of viral infection.

As reported in the May 4, 2011, advance online edition of the Journal of Virology, the researchers did not detect XMRV or related MLVs, or antibodies against these viruses, in any of their patient samples. Furthermore, they also performed a blinded analysis of stored samples from CFS patients in the Mikovits study, but again found no evidence of XMRV infection.

"Our experience has taught us that the detection of XMRV in blood is fraught with difficulties," the researcher wrote, explaining that different laboratory techniques yielded conflicting results and suggesting contamination may play a role. Positive readings were initially obtained using a "biorobot," but when this equipment was abandoned XMRV was no longer detected.

"Given the lack of evidence for XMRV or XMRV-like viruses in our cohort of CFS patients, as well as the lack of these viruses in a set of patients previously tested positive, we feel that that XMRV is not associated with CFS," they continued. "We are forced to conclude that prescribing antiretroviral agents to CFS patients is insufficiently justified and potentially dangerous."

However, they added, "It is also vital to state that there is still a wealth of prior data to encourage further research into the involvement of other infectious agents in CFS, and these efforts must continue."

"Chronic fatigue syndrome is a devastating disease for which a cure needs to be found," Singh said in a press release issued by University of Utah Health Sciences.